In FIG. 7, the basic construction of a dynamic drive type dot matrix display device is shown. In this display, along with the common lines CL0, CL1, CL2, CL3 that extend in the horizontal direction as scanning electrodes arranged at a fixed pitch in the vertical direction, the signal lines RL0, RL1, RL2, RL3 that extend in the vertical direction as signal electrodes are arranged at a fixed pitch in the horizontal direction, and LEDs (light emitting diodes) are arranged with the anodes connected to the common lines CL) and the cathodes connected to the signal lines RL, respectively, as display elements at each intersection point of a matrix.
The common lines CL0, CL1, CL2, CL3, are electrically connected to the terminal of the positive polarity power supply voltage VBB through the medium of the switches K0, K1, K2, K3, respectively. On the other hand, the signal lines RL0, RL1, RL2, RL3, are electrically connected to the ground terminal through the medium of the switches F0, F1, F2, F3 and the fixed current source circuits (active loads) J0, J1, J2, J3, respectively.
Within one frame cycle, the common lines CL0, CL1, CL2, CL3 are driven (supplied electricity) by the power supply voltage VBB in a time division manner by means of selective control of the switches K0, K1, K2, K3. Normally, the common lines CL0, CL1, CL2, CL3 are driven (supplied electricity) by the power supply voltage VBB for a constant period (horizontal scanning period) sequentially and selectively from top to bottom according to a line sequence scanning. Then, in each horizontal scanning period, the switches F0, F1, F2, F3 are turned ON for just the time responding to the respective corresponding signals (for example, the gradation signals that designate the gradations of the pixels), and one line portion of the LEDi0, LEDi1, LEDi2, LEDi3 that are connected to the selected common line CLi emit light by conducting a prescribed current for just the ON time of each corresponding switch F0, F1, F2, F3.
As mentioned above, theoretically, the display device becomes an assembly wherein only the LEDi0, LEDi1, LEDi2, LEDi3 on the one line of the common lines CLi that has been selected emit light at one time. But, in this type of display used in the past, there are instances LEDj1, LEDj2, LEDj3 on other common lines CLj that have not been selected are caused to emit undesired erroneous lighting.
An explanation will be given for the cause of the above-mentioned erroneous lighting phenomenon based on the abbreviated model of FIG. 8. This model is a minimum 2×2 matrix, and a display pattern is assumed wherein only the LED00 and LED11 on the diagonal line are caused to repeatedly light, and the other LED01 and LED10 are maintained in the extinguished state. In this case, the non-display LED01, LED10 equivalently function as condensers Cap01, Cap10.
In the first horizontal scanning period, K0=ON, K1=OFF, F0=ON, F1=OFF and LED00 is lit, and LED01 (Cap01) is charged. Here, at the LED01 (Cap01), the common line (CL0) on the anode side is supplied with electricity by the power supply voltage VBB, and the signal line SL1 on the cathode side is placed in a floating state. Because of this, all the negative electrical charge that is present on the signal line RL1 is collected at the cathode electrode of the LED01 (Cap01), and the LED01 (Cap01) is charged by just that collected charged quantity. The voltage between the anode and cathode of the LED01 (Cap01) at this time, in other words, the charging voltage (Vcap), is determined by means of this charging load quantity. Since the anode electrode of the LED01 (Cap01) becomes the same as the potential of the power supply voltage VBB, the potential of the cathode electrode of the LED01 (Cap01), in other words, the potential VRL1 for the signal line RL1 is VRL1=VBB−Vcap.
Next, in the second horizontal scanning period, K0=OFF, K1=ON, F0=OFF, F1=ON and LED11 is lit, and LED10 (Cap10) is charged. The LED00 is extinguished, and temporarily (while extinguished) can be viewed as a condenser. LED01 (Cap01) becomes a problem at this time. Due to the fact that the switch F1 is closed, the negative charge that accumulated at the cathode electrode of the LED01 (Cap01) is shifted to the ground through the signal line SL1. On the other hand, because the switch K0 is open, the positive charge that has accumulated at the electrode of the LED01 (Cap01) dies out through a DC escape path. Because of that, the potential difference Vcap between the two electrodes of the LED01 (Cap01) suddenly increases, and the LED01 that was equivalent to a condenser up until then conducts and lights. As expected, when the Vcap drops below the threshold value for the LED01, the conduction (lighting) stops. In any case, during the second horizontal scanning cycle, the LED01 that originally should not light erroneously lights with capacitance noise being the cause, without relationship to the signal.
In the first horizontal scanning period, the LED10 that was originally not supposed to light is caused to emit an erroneous lighting in the same manner as mentioned above. This type of erroneous lighting is weak compared to the normal lighting condition, but is recognizable to the human eye, and is a problem with respect to the quality of the display.
An aspect of this invention was achieved by referring to the above-mentioned problem points, and an object is to offer a dot matrix display device in which the erroneous display of display elements that are connected to a scanning electrode during non-selection in the scanning of the dynamic drive system is effectively prevented, so the display quality is improved.